This invention relates generally to a blade outer air seal for a gas turbine engine. More particularly, this invention relates to a blade outer air seal with improved cooling features.
A gas turbine engine includes a compressor, a combustor and a turbine. Compressed air is mixed with fuel in the combustor to generate an axial flow of hot gases. The hot gases flow through the turbine and against a plurality of turbine blades. The turbine blades transform the flow of hot gases into mechanical energy to rotate a rotor shaft that drives the compressor. A clearance between a tip of each turbine blade and an outer air seal is preferably controlled to minimize flow of hot gas therebetween. Hot gas flow between the turbine tip and outer air seal is not transformed into mechanical energy and therefore negatively affects overall engine performance. Accordingly, the clearance between the tip of the turbine blade and the outer air seal is closely controlled.
The outer air seal is exposed to the hot gases and therefore requires cooling. The outer air seal typically includes an internal chamber through which cooling air flows to control a temperature of the outer air seal. Cooling air is typically bleed off from other systems that in turn reduces the amount of energy that can be utilized for the primary purpose of providing thrust. Accordingly it is desirable to minimize the amount of air bleed off from other systems to perform cooling. Various methods of cooling the outer air seal are currently in use and include impingement cooling where cooling air is directed to strike a back side of an outer surface exposed to hot gases. Further, cooling holes are utilized to feed cooling air along an outer surface to generate a cooling film that protects the exposed surface. Each of these methods provides good results. However, improvements in gas turbine engines have resulted in increased temperatures and more extreme operating conditions for those parts exposed to the hot gas flow.
Accordingly, there is a need to design and develop a blade outer air seal that utilizes cooling air to the maximum efficiency to both increase cooling effectiveness and reduce the amount of cooling air required for cooling.